The present invention is generally directed to soft, solvent resistant and elastic wiping products and to a method for making the wiping products. More particularly, the present invention is directed to wiping products made from a web which has been creped at least once and which contains thermally bonded synthetic fibers. By including the thermally bonded fibers within the web, the wiping product can be made without the use of latex adhesives as were conventionally used in the past.
Disposable wiper products such as paper towels, industrial wipers, and other similar products are designed to include several important properties. For example, the products should have good bulk, a soft feel and should be highly absorbent. The products should also have good strength even when wet and should resist tearing. The wiping products should also have good stretch characteristics, should be abrasion resistant, and should not deteriorate in the environment in which they are used.
In the past, many attempts have been made to enhance and increase certain physical properties of disposable wiping products. Unfortunately, however, when steps are taken to increase one property of a wiping product, other characteristics of the product may be adversely affected. For instance, in cellulosic based wiping products, softness is typically increased by decreasing or reducing cellulosic fiber bonding within the paper product. Inhibiting or reducing fiber bonding, however, adversely affects the strength of the paper web.
One particular process that has proven to be very successful in producing paper towels and other wiping products is disclosed in U.S. Pat. No. 3,879,257 to Gentile, et al., which is incorporated herein by reference in its entirety. In Gentile, et al., a process is disclosed for producing soft, absorbent, single ply fibrous webs having a laminate-like structure that are particularly well suited for use as wiping products.
The fibrous webs disclosed in Gentile, et al. are formed from an aqueous slurry of principally lignocellulosic fibers under conditions which reduce interfiber bonding. A bonding material, such as a latex elastomeric composition, is applied to a first surface of the web in a spaced-apart pattern. In particular, the bonding material is applied so that it covers from about 50% to about 60% of the surface area of the web. The bonding material provides strength to the web and abrasion resistance to the surface. Once applied, the bonding material can penetrate the web preferably from about 10% to about 40% of the thickness of the web.
The bonding material can then be similarly applied to the opposite side of the web for further providing additional strength and abrasion resistance. Once the bonding material is applied to the second side of the web, the web can be brought into contact with a creping surface. Specifically, the web will adhere to the creping surface according to the pattern to which the bonding material was applied. The web is then creped from the creping surface with a doctor blade. Creping the web greatly disrupts the fibers within the web, thereby increasing the softness, absorbency, and bulk of the web.
In one of the preferred embodiments disclosed in Gentile, et al., both sides of the paper web are creped after the bonding material has been applied. Gentile, et al. also discusses the use of chemical debonders to treat the fibers prior to forming the web in order to further reduce interfiber bonding and to increase softness and bulk.
The processes as disclosed in Gentile, et al. have provided great advancements in the art of making disposable wiping products. The products, however, tend to be somewhat expensive to produce due in part to the cost of the latex bonding material that is applied to each side of the web and due to the equipment and energy requirements needed to apply and cure the bonding material. Further, besides being one of the more expensive components of the product, in some applications, the latex bonding material when cross-linked and cured may form formaldehyde. When formaldehyde is formed, precautions must be taken to ensure that the formaldehyde does not create any health risks and is not released to the environment.
Thus, it would be desirable if disposable wiping products having properties similar to those disclosed in Gentile, et al. could be produced without using a latex bonding material. More particularly, a need exists for a method of producing wiping products having good softness, bulk, absorbency and strength that can be made without having to use a latex adhesive. A need also exists for a method of producing wiping products that will not degrade significantly when exposed to solvents and chemicals as will be described in more detail hereinafter.
The present invention recognizes and addresses the foregoing drawbacks, and deficiencies of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved method for producing wiping products.
Another object of the present invention is to provide wiping products that can be made without the use of a latex bonding material or adhesive.
It is another object of the present invention to provide a method for producing wiping products that are soft and absorbent while having good strength and stretch characteristics when either wet or dry.
Still another object of the present invention is to provide a wiping product that contains binder fibers that thermally bond together when heated under pressure.
It is another object of the present invention to provide a method for producing wiping products by incorporating into a paper web binder fibers which, when heated, adhere to a creping surface for allowing the paper web to be creped without the use of an adhesive.
Another object of the present invention to provide a method for producing wiping products that do not have to be fed through a high temperature curing oven when being produced.
These and other objects of the present invention are achieved by providing a method for producing wiping products that includes first providing a web of material that contains binder fibers. The binder fibers are capable of thermally bonding together when heated above a softening temperature and pressed together.
The method further includes the step of adhering one side of the web to a creping surface. In particular, the web is placed in contact with the creping surface while the web is at a temperature greater than the softening temperature of the binder fibers but at a temperature insufficient to melt the fibers. The first side of the web is then creped from the creping surface causing interfiber bonding to occur between the binder fibers, while also increasing softness, absorbency and bulk of the web.
In one embodiment, the web is adhered to the creping surface through the use of the binder fibers without using an adhesive, such as a latex adhesive. The binder fibers can comprise polyolefin fibers, such as polyethylene fibers or polypropylene fibers. The binder fibers can also be bicomponent fibers including a core polymer surrounded by a sheath polymer. When using bicomponent fibers, the core polymer should have a melting temperature higher than the melting temperature of the sheath polymer.
The binder fibers can be present within the web in an amount of at least about 5% by weight, and particularly in an amount of from about 5% by weight to about 60% by weight. Besides binder fibers, the web can also include pulp fibers, such as softwood fibers. In order to cause the binder fibers to adhere to the creping surface, the creping surface can be heated to a temperature of from about 290xc2x0 F. to about 325xc2x0 F.
In one alternative embodiment, the method can further include the step of embossing a pattern into the web as the web is adhered to the creping surface.
These and other objects of the invention are also achieved by providing a method for producing wiping products including the steps of first providing a web of material containing binder fibers capable of thermally bonding together when heated above a softening temperature and pressed together. The binder fibers can be made containing either polyethylene or polypropylene. The binder fibers are present within the web in an amount of at least about 5% by weight.
A first side of the web is contacted with a first heated creping surface. The creping surface is heated to a temperature sufficient to cause the binder fibers contained in the web to adhere to the surface but to a temperature insufficient to melt the binder fibers. Once adhered to the creping surface, the web is creped from the surface.
The second side of the web is then similarly contacted with a second heated creping surface. The second creping surface is also heated to a temperature sufficient to cause the binder fibers contained in the web to adhere to the surface but at a temperature insufficient to melt the fibers. Once adhered to the second creping surface, the second side of the web is creped for producing the wiping product.
Of particular advantage, the web of material can be adhered to both the first creping surface and to the second creping surface without using an adhesive. In one embodiment, a first press roll can be used to place the first side of the web into contact with the first creping surface and a second press roll can be used to place the second side of the web into contact with the second creping surface. The first press roll and the second press roll exert pressure on the web in an amount sufficient to adhere the web to the creping surfaces. In one embodiment, at least one of the press rolls can emboss a pattern into the web as the web is adhered to one of the creping surfaces.
Creping each side of the web increases the web""s bulk and absorbency, as well as its softness and compressibility. According to the present invention, the creping action also serves to cause the heated binder fibers to bond together, thus also increasing the strength and elasticity of the web.
The wiping products produced according to the above processes can have a basis weight of from about 15 pounds per 2,880 square feet to about 100 pounds per 2,880 square feet.
Other objects, features, and aspects of the present invention are discussed in greater detail below.